Field of the Invention
The present invention relates to an image forming apparatus of electrophotographic type or electrostatic recording type.
Description of the Related Art
An image forming apparatus of in-line color type including a plurality of image forming stations aligned along the rotational direction of an intermediate transfer member is known as an image forming apparatus such as a laser beam printer. Each of the image forming stations of such an image forming apparatus includes an image bearing member and develops an electrostatic latent image formed thereon by using a developing unit. Then, each image forming station primarily transfers a developed developer image from the image bearing member onto the intermediate transfer member. A plurality of the image forming stations repeats the same process to form a color developer image on the intermediate transfer member. Subsequently, the color developer image is secondarily transferred onto a recording material such as paper, and a fixing unit fixes the color developer image onto the recording material.
The image to be generated on the recording material in a series of image forming operations needs to be output satisfying the image and density desired by the user. Color reproducibility and stability are required for a full color image (color developer image) generated by a plurality of the image forming stations.
Japanese Patent Application Laid-Open No. 11-38750 discusses a technique for forming a plurality of patches on a photosensitive drum serving as an image bearing member while the rotational speed of a developing sleeve is varied, detecting a patch having reached a required density out of a plurality of the patches, and determining the rotational speed of the developing sleeve.
Japanese Patent Application Laid-Open No. 8-227222 discusses a technique for changing a developing bias and changing the rotational speed of a developer bearing member such as a development roller to extend a color selection range.
The invention discussed in Japanese Patent Application Laid-Open No. 8-227222 is configured to increase the amount of developer supplied from the developer bearing member such as the developing roller to an image bearing member such as a photosensitive member to extend the color selection range.
In a case where the color selection range is extended by increasing the developer amount per unit area on such an image bearing member, a detection unit for detecting the developer amount is unable to detect the developer amount with sufficient accuracy in some cases.